The present invention relates to electric machines and preferably to machines having a slot-wound stator. The invention comprises a method for the production of such stators.
Alternating current induction motors and generators are usually made with slot-wound stators, the winding of which is fixed by immersing or dipping. The rotor is journalled in bearing shields which are centered on the outer diameter of the stator or in a housing combined with the stator. Usually the housing and the bearing shields make a closed motor housing, the outer side of which is cooled by a fan mounted at the end of the axis.
The market for smaller mass-produced induction motors is characterized by a tough price competition at the same time as the requirements on reliability and silent function are high.
This has given rise to an extended mechanization combined with a simplification of the construction of the motors. As a part of the effort for simplification and cost reduction one has during recent years made many attempts to mould in bearing shields and stator housings in one operation by moulding in the stator with plastic mass and at the same time impregnating the stator winding. The moulding methods which then have been used are injection moulding according to the transfer method, moulding according to the pressure-gel method, moulding under vacuum, and centrifugal moulding with moulds arranged outside the center on a rotating disc. None of these moulding methods have, however, given the combination of properties of the finished motor and the economy in the production method, that are required to get substantial advantages compared to existing conventional production methods.
If a motor having plastic moulded stator shall give sufficient advantages above conventional motors, the construction and the production method must fulfill the following conditions:
Accurate and durable centering of the rotor for obtaining a silent and vibration-free function;
Efficient cooling of the windings and bearings to make a high power output per material volume possible;
Guaranteed minimum distance between stator windings and touchable surface on the motor to fulfill the security regulations;
Complete and cavity-free impregnation of the whole stator winding;
Minimum consumption of plastic material;
Quick and reliable moulding method with reasonable machine investment; and
Minimum tool inventment and simple change between different lengths of the stators.
The above mentioned moulding methods have all that in common that they only partly fulfill these requirements. In no case the different requirements are fulfilledd to such an extent that the total production economy is satisfactory.